I have just designed a prototype Arm 9 based board that uses a Davicom DM9161 ethernet chip operating in RM11 mode, basically it require a external 50MHz oscillator that feeds it and the MAC in the processor. The board has just failed EMC emissions at 50MHz and 100MHz which are due to the ethernet, disconnectioning but still running the 50MHz ethernet oscillator made it pass. We have the option on the redesign of using MII ethernet mode, which uses a 25Mhz crystal into the DM9161, though internally a 100MHz clock is still required, the communications to the MAC is then at 25MHz (100Base) and comes from the DM9161 TXCLK and RXCLK. Would you expect doing this would reduce the EMC emission problems at 50 and 100MHz? Thanks for any advice
Steve jones